Dual-edge sampling with k-clock to avoid aliasing in optical coherence tomography
Techniques and apparatus for producing sampled Optical Coherence Tomography (OCT) interference signals without aliasing, based on a swept-source OCT interference signal. An example apparatus comprises a k-clock circuit configured to selectively output a k-clock signal at any of a plurality of k-clock frequencies ranging from a minimum k-clock frequency to a maximum k-clock frequency, and an anti-aliasing filter configured to filter a swept-source OCT interference signal, to produce a filtered OCT interference signal, where the anti-aliasing filter has a cut-off frequency greater than one-half the minimum k-clock frequency but less than the minimum k-clock frequency. The apparatus further comprises an analog-to-digital (A/D) converter circuit configured to sample the filtered OCT interference signal at twice the k-clock frequency, to produce a sampled OCT interference signal. In some embodiments, the A/D converter circuit samples the filtered OCT interference signal at both rising and falling edges of the k-clock signal.
1. An Optical Coherence Tomography (OCT) data acquisition and processing circuit for use in producing an OCT image based on a swept-source OCT interference signal, the OCT data acquisition and processing circuit comprising:
a k-clock configured to selectively output a k-clock signal at any of a plurality of k-clock frequencies ranging from a minimum k-clock frequency to a maximum k-clock frequency;
an anti-aliasing filter configured to filter the swept-source OCT interference signal, to produce a filtered OCT interference signal, the anti-aliasing filter having a cut-off frequency greater than one-half the minimum k-clock frequency but less than the minimum k-clock frequency; and
an analog-to-digital (A/D) converter circuit coupled to an output of the anti-aliasing filter and configured to sample the filtered OCT interference signal at twice the k-clock frequency, to produce a sampled OCT interference signal;
wherein the A/D converter circuit comprises first and second A/D converters, the first A/D converter being configured to sample the filtered OCT interference signal at the k-clock frequency, using the k-clock signal, and the second A/D converter being configured to separately sample the filtered OCT interference signal at the k-clock frequency, using a phase-shifted replica of the k-clock signal, the A/D converter circuit further comprising a multiplexer to combine the sampled outputs from the first and second A/D converters to obtain the sampled OCT interference signal.
2. An OCT system comprising the OCT data acquisition and processing circuit of claim 1 , and further comprising:
a swept optical source; and
an interferometer coupled to an output of the swept optical source, the interferometer comprising a detector circuit configured to generate the swept-source OCT interference signal from an optical interference signal produced by the interferometer.
3. An OCT system comprising the OCT data acquisition and processing circuit of claim 1 , and further comprising:
a digital signal processing circuit configured to process the sampled OCT interference signal to obtain an OCT image; and
a display configured to display the OCT image.
4. The OCT data acquisition and processing circuit of claim 1 , further comprising:
a k-clock doubler configured to produce the phase-shifted replica of the k-clock signal.
5. An Optical Coherence Tomography (OCT) data acquisition and processing circuit comprising:
a k-clock configured to selectively output a k-clock signal at any of a plurality of k-clock frequencies ranging from a minimum k-clock frequency to a maximum k-clock frequency;
a k-clock doubler configured to produce a phase-shifted replica of the k-clock signal;
an anti-aliasing filter configured to filter the swept-source OCT interference signal, to produce a filtered OCT interference signal, the anti-aliasing filter having a cut-off frequency greater than one-half the minimum k-clock frequency but less than the minimum k-clock frequency;
first and second A/D converters, the first A/D converter being configured to sample the filtered OCT interference signal at the k-clock frequency, using the k-clock signal, and the second A/D converter being configured to separately sample the filtered OCT interference signal at the k-clock frequency, using the phase-shifted replica of the k-clock signal, the A/D converter circuit further comprising a multiplexer to combine the sampled outputs from the first and second A/D converters to obtain the sampled OCT interference signal;
a digital signal processor, an input of the digital signal processor coupled to an output of the analog-to-digital (A/D) converter circuit;
the multiplexer coupled to an output of the first A/D converter and to an output of the second A/D converter; and
the digital signal processor coupled to an output of the multiplexer.
6. An OCT system comprising the OCT data acquisition and processing circuit of claim 5 , and further comprising:
a swept optical source; and
an interferometer coupled to an output of the swept optical source, the interferometer comprising a detector circuit configured to generate the swept-source OCT interference signal from an optical interference signal produced by the interferometer.
7. An OCT system comprising the OCT data acquisition and processing circuit of claim 5 , and further comprising:
a digital signal processing circuit configured to process the sampled OCT interference signal to obtain an OCT image; and
a display configured to display the OCT image.